Human bodies moving in unison to form a grand design create a very accessible pleasure. The shapes and patterns that constitute the human kaleidoscope of a Busby Berkeley number or a synchronised swimming routine are easy on the eye and need make no intellectual demands on the viewer. The audience can lie back and watch the pretty patterns while the music washes over them. Peggy Spencer, doyenne of formation ballroom dancing, makes no apology for unison's easy appeal: "The spectacle is so much easier to absorb.You see the whole scene in a comfortable glance, you don't get tennis neck trying to look at it."

Formation dancing confirms one of the golden rules of theatre: massed mediocrity can be every bit as spectacular as individual virtuosity. Unison is everywhere and the public's appetite for it has long been inexhaustible: can-can, Mrs Tiller's girls, Trooping the Colour, Riverdance, synchronised swimming, the classical corps de ballet. All appeal to the human eye's delight in patterning. A true balletomane might question ballet's place on that list but there has always been an element of the ballet audience that is more interested in the precision-drilled spectacle than the plastique. Indeed, there was a time when the audience's interest was even less aesthetic. In the last century, the tantalising prospect of girls galore had a basic appeal in a world where a red-blooded male was lucky to glimpse the legs on a piano. The idea that 72 pink silk knees and thighs might be available for inspection in a respectable theatre made the ballet blanc irresistible and every production had its vision scene complete with a few dozen girls doing relatively simple things to form ingenious designs. Critics at the time were not always happy with these ballabiles, arguing that they weren't in the spirit of the true ballet d'action but owed more to the inferior "ballets feeries", plotless, pulchritudinous extravaganzas that were the ancestors of follies and revues.

In fact, in the hands of a master like Petipa or Ivanov, an apparently irrelevant interlude featuring more pretty girls than would normally be rational or desirable could be transformed into a work's most enduring image and, on a good night, the symphonic white act could transcend the merely well-drilled and approximate the sublime. The vision scene in La Bayadere, and the lakeside scenes of Swan Lake with their ghostly squadrons of women in white, are classic examples of this masterly use of massed effect.

OK. Big is Beautiful. But surely size isn't everything? Surely the ballet's beauty and significance doesn't increase exponentially as one lengthens the cast list? Isn't there a critical point at which the aesthetic response gives way to sheer amazement that the world affords that many pretty women? English National Ballet's new production of Swan Lake which opens at the Royal Albert Hall on Thursday will feature 65 swans. The critics' knives are out and words like "circus" and "dumbing down" are being used with abandon. This is not helped by the company's proud boast that 1,000 metres of net will be required for the tutus - an unwelcome echo of ballroom dancing trivia. Next they'll be telling us that Derek Deane's mother is sewing on all the sequins by hand. The other, possibly more valid, concern is that classical ballet cannot be made in the round. The Albert Hall's most recent forays into ballet presentation have not been a critical success. In 1993, the Bolshoi, lacking time to rebuild their ballets from scratch, "adapted" them for performance on a thrust stage but the views from the sides were appalling. Derek Deane admits to finding the Bolshoi's Albert Hall venture "vulgar" and "brash" but insists that, when choreographed specifically for the arena, it will work. "There is no need to turn classical ballet into a circus. This Swan Lake is just a large version of a classical production. It's wrong to compare it with a proscenium arch production. To say 'you have to have a proscenium arch to see ballet properly' is a bit pretentious. It's important to experiment." Patrick Deuchar, chief executive of the Albert Hall, has enjoyed huge commercial success with arena operas like the recent Carmen and has been trying to get arena ballet into the Hall for a while. The argument that ballet is a pictorial rather than a sculptural spectacle cuts no ice with him at all: "I view these things through arena spectacles. I apply a different set of rules."

Ballet itself originated as an arena spectacle in the ballrooms of the French court. However, it soon became a theatrical form and its steps and its productions were conceived and developed with a perspective stage in mind. Built into the choreography was the assumption of an ideal point of view (roughly the middle of the dress circle, hence the high prices). Peggy Spencer, used to performing in the round, is unhappy with theatrical dance: "I once had a long talk with Nureyev about this. It becomes very elitist because there's always an ideal position to see from. At the Albert Hall everyone can see."

Well that's the plan, anyway. Derek Deane, armed with a scale model of the auditorium and hundreds of pennies, is making arrangements for our entertainment. He is adamant that the result will tread the fine line between art and showbiz and, although he respects the hard work that goes into other massed spectacles, he insists that his jumbo Swan Lake is in a different class. "I can watch ballroom dancing for 15, maybe 20 minutes. It does make me giggle - the look, the hair, the permanent grin - but, God, it's bloody difficult. Riverdance? I only managed 20 minutes. It was very clever, very precise and for certain people that's enough entertainment, I suppose. Synchronised swimming is about shape, pattern and timing. It's not about feelings, it's not about telling a story. I've got 65 swans bourreeing and that can make you cry." Patrick Deuchar, the master of understatement, confides, "Derek has an exuberant confidence level."

Deane is actually less than happy at having to use 65 swans. He wanted 70. A normal English National Ballet production of Swan Lake contains a mere 22 birds and recruitment has been a nightmare. Once assembled, the differences between the dancers became painfully apparent: "It's very difficult when you have people from so many different schools. We have tried to correct people's epaulement, correct their legs and feet. We've had to get them all to work together musically, to breathe through the movement, which gives the dancing a different quality."

If anyone can knock them into shape it's Deane. In his four years as ENB's artistic director he has transformed the general standard of dancing: "When I came to this company it was at a physical low ebb. People who were coming for auditions had no stomachs, no backs, no legs." He has transformed these human jellies into an impressive corps de ballet. His efforts have been rewarded by a series of coups that make you wonder if a fairy godmother (or a Mephistopheles?) is at work: the company has won a sexy Prudential Award; Altynai Asylmuratova, the greatest Russian ballerina of her generation, will lead the cast of Swan Lake on Thursday and his company, shoehorned on to the cramped Royal Festival Hall stage since 1951, can now wave goodbye to "that dreadful place" and stretch awake at the palatial London Coliseum and the Royal Albert Hall. Meanwhile, Deane's London rivals at Covent Garden, having dragged their feet over arrangements for alternative London venues during the theatre's closure, will be camping out at the Barbican and Festival Hall. Derek Deane is far too nice a chap not to have fellow feeling for his former Royal Ballet colleagues but he isn't exactly losing sleep over their plight. His company, with a businesslike approach that contrasts so revealingly with the aristocratic indecision of Covent Garden, has scooped London's finest venues and Russia's greatest ballerina. Derek Deane can barely contain his glee: "You cannot imagine how pleased we are."

Right now Deane's only worry is marshalling his 65 swans through countless rehearsals in the Albert Hall. Peggy Spencer is very sympathetic. "The Albert Hall to us was a nightmare because you've got to arrange your patterns to fit a circle." Her formation dances usually featured a mere eight couples but she has been known to mastermind as many as 300 at Earls Court. Give her somewhere to stand and she could mass-choreograph the world.

'Swan Lake' is at the Royal Albert Hall, London SW7, from 29 May to 11 June (0171-589 8212)

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